1. Field of the Invention
This invention relates to a method useful for storing crude oil and transporting crude oil. This invention particularly relates to a method for storing crude oil and transporting crude oil in tanks and through pipes and pipelines.
2. Background of the Art
Many formation fluids such as petroleum fluids contain a large number of components with a very complex composition. Some of the components present in production fluid, for example wax and asphaltenes, are normally solids under ambient conditions, particularly at ambient temperatures and pressures. Asphaltenes are typically dark brown to black-colored amorphous solids with complex structures and relatively high molecular weight. In addition to carbon and hydrogen, asphaltenes also can contain nitrogen, oxygen and sulfur species. Typical asphaltenes are known to have some solubilities in the production fluid itself or in certain solvents like carbon disulfide, but are usually insoluble in solvents like light naphthas.
When the formation fluid from a subsurface formation comes into contact with a pipe, a valve or other production equipment of a wellbore or when there is a decrease in temperature, pressure, or change of other conditions, asphaltenes may precipitate or separate out of a well stream or the formation fluid while flowing into and through the wellbore to the wellhead. While any asphaltene separation or precipitation is undesirable in and by itself, it is much worse to allow the asphaltene precipitants to accumulate by sticking to the equipment in the wellbore. Any asphaltene precipitants sticking to the wellbore surfaces may narrow pipes; and clog wellbore perforations, various flow valves, and other wellsite and downhole equipment.
For purposes of the present invention, the term “crude oil” means the petroleum fluids produced from an oil well. Typically, the crude oil produced from an oil well is treated to remove excess water and inorganic solids such as salt and then collected and stored for shipment to a refinery. Often, the crude oil from several fields can be accumulated at a central point for shipping through a pipeline.
Precipitations and accumulations of asphaltenes in a pipeline for transferring crude oil could result in loss of oil flow and/or equipment failure. Crude oil storage facilities could have maintenance or capacity problems if asphaltene precipitations occur during shipping of crude oil. Precipitation of asphaltene during shipping is clearly just as undesirable as during production. As a result of these potential problems, many chemicals, also referred to herein as “additives”, including solvents, are available to prevent or control the precipitation of asphaltenes. Often, by the time a crude oil reaches a shipping center, it may contain at least some of these additives.
It would be desirable in the art of shipping crude oil by pumping the crude oil through pipelines to minimize the precipitation of asphaltenes during shipping. It would also be desirable if the more than one crude oil could be blended and then so shipped while still minimizing the precipitation of asphaltenes. It would be even more desirable if these objectives could be achieved while saving chemical and energy costs.